Hi,
Since i haven't found any solution for this, i just wrote a little program.
It will check your external ip and update the tunnel endpoint if necessary.
Get it @ http://www.itsecsys.com/Pages/TunnelbrokerIPV6Updater.aspx (http://www.itsecsys.com/Pages/TunnelbrokerIPV6Updater.aspx)
Feedback is welcome !!